The unprecedented leak of top-secret documents by National Security Agency contractor Edward Snowden raises far-reaching questions about the government’s rush to outsource intelligence work to contractors since the Sept. 11, 2001, terrorist attacks.

Never before have so many U.S. intelligence workers been hired so quickly, or been given access to secret government information through networked computers. In recent years, about one in four intelligence workers has been a contractor, and 70 percent or more of the intelligence community’s secret budget has gone to private firms.Booz Allen Hamilton, which hired the 29-year-old Snowden three months ago to work at the NSA, has been a leader among more than 1,900 firms that have supplied tens of thousands of intelligence analysts in recent years, including technologists and field spies.